1. Field of the Invention
The present invention relates to a molding method, which comprises steps of an injection molding of a molded product using a synthetic resin and successive compression spread molding of a decorative film over a surface of the molded product using a coating material.
2. Description of the Related Art
In a method so-called In-Mold Coat Molding, a decorative film of a coating material is molded over a surface of a molded product of a synthetic resin. In this method, a cavity mold for the injection molding is also used as that for the decoration molding.
For example, JP 2001-38783A discloses a conventional molding method, which comprises providing an injection cavity mold and a core to form a cavity for a molded product; injecting a melted resin fully into the cavity to form the molded product; moving the core slightly backward to form a desired space between the surface of the molded product and the surface of the cavity; and injecting a decorative coating material into the space to form a decorative film.
In such the conventional molding method that employs the injection cavity mold commonly in two types of molding for the molded product and the decorative film, the cavity mold and the core are set at a hardening temperature of a thermoplastic resin for injection molding of the product. Therefore, if the coating material is composed of a thermoplastic resin composition, there is no difficulty in temperature control of the cavity mold. To the contrary, if the coating material is composed of a thermosetting composition, it is required to elevate the temperature in the cavity mold up to a thermosetting temperature of the coating material in a short time after the injection molding.
The hardening temperature of the thermoplastic resin set on the cavity mold and the core has a difference from the thermosetting temperature of the coating material. This temperature difference varies depending on the material resin of the molded product and the substrate of the coating material though it has a value of at least 30° C. or more. It is considered technically difficult to elevation control such the temperature difference in a limited molding time. Therefore, the conventional molding method that employs the injection cavity mold commonly for the two types of molding has a problem because it is hardly utilized in decoration molding using a thermosetting coating material.
The space for molding the decorative film is formed in retreating operation of a movable table that carries the core attached thereon or a moving device located inside the table. Therefore, the formation of the space requires a sophisticated positioning control and a means for retaining the space. In addition, the formation of the space by the retreat of the core is limited in between opposing surfaces: a front surface of the molded product and a surface of the cavity. In this case, vertical sides of the product are in parallel with the moving direction of the core and keep in contact with the cavity surface without forming any space therebetween. Therefore, it is impossible to mold a decorative film over vertical sides of a box-like molded product, resulting in a problem because the decoration molding is restricted in products molded in limited shapes.
The problem associated with the common use of the mold can be solved by the use of individual molds for injection molding of the product and molding of the decorative film. In the molding of the decorative film by injecting a coating material, the coating material may contain fine flat shiny materials such as aluminum pigment to exhibit a metallic painting color. In this case, when the coating material is injected into the cavity, the aluminum pigment vigorously collide with each other at a welded portion, varying the orientation and distribution of aluminum pigment easily, and causing lines and variations of aluminum pigment distribution disadvantageously.
The decoration cavity mold is set at a temperature as high as 80° C. or more to thermoset the coating material. It is required to thermally insulate the supply gate and passage for the coating material connected to the cavity so as not to precure the coating material by the heat from the cavity mold. As a result, the decoration cavity mold has a complicated structure and is hardly controlled.
The present invention has an object to provide a new method of injection molding and compressive decoration molding a molded product. This method employs individual cavity molds for injection molding a molded product and for decoration molding a surface of the molded product by compression spreading successively in order to solve the problems associated with the conventional common use of the mold and with the injection to the common mold. It is capable of efficiently molding a decorative film with a thermosetting coating material under suitable temperature control regardless of the shapes of injection molded products.